1. Field of the Invention
This invention relates to spark wheels of the type used for generating sparks to ignite fuel in cigarette lighters and the like, and is directed more particularly to methods of forming the abrasive surfaces on spark wheels.
2. Description of the Prior Art
Spark wheels of the type used in cigarette lighters are usually cylindrical and have an abrasive peripheral surface. The abrasive surface generally comprises a series of teeth or ridges which are arranged in a series of rows across the surface and which extend up from the surface in a common inclined direction. The rotation of such a wheel against a flint generates the fine particles which by rapid oxidation create sparks necessary to ignite a fuel.
Manufacturing processes for toothed spark wheels of the type above described generally involve two stages for the formation of the teeth. In the first stage spiral grooves (leaving lands therebetween) are formed in the peripheral surface of a wheel blank, typically in a screw machine. In a second stage another set of grooves in the periphery of the wheel is formed typically by cold chiseling, along lines generally parallel to the axis of the wheel, the intersecting sets of grooves and lands defining individual sharp cutting teeth. Spark wheels so formed are then generally subjected to a suitable hardening process for increased service life. Although spark wheels made in this manner can provide good sparkig performance, such processes are generally slow and consequently expensive to carry out, since many separate strokes of the chiseling tool are required to form the teeth on each wheel.
Another process utilizing a similar first stage and a simplified second stage (for example as disclosed in U.S. Pat. No. 2,455,348) involves forming all the grooves parallel to the axis of the wheel in a single operation by forcing the grooved wheel once through a broaching die. While this process is relatively efficient, there is the disadvantage that the individual teeth so formed are not very sharp, especially with increasing die wear, and spark wheels formed in this manner rely to a substantial degree for their effective operation on the numerous burrs which are created along the edges of the teeth in the single broaching operation.